In recent years, the relationships between diseases and RNAs such as blood microRNAs have been drawing attention, and attempts have been made to utilize detection of RNAs in medical care for early disease detection and the like.
As a method of quantifying a microRNA, for example, there has been reported a method of specifically amplifying a target microRNA by polymerase chain reaction (PCR) and detecting the target microRNA (Japanese Patent No. 5192229). However, because of the necessity of performing PCR, for example, it is necessary to use a temperature-controlling apparatus and to perform reverse transcription into DNA, which makes the operations complicated. Moreover, in the above-described method, DNA is obtained from the RNA contained in a small amount of sample through reverse transcription and further amplified by PCR. Such reverse transcription PCR is, however, not direct detection but indirect detection of the RNA contained in the sample; therefore, there is a problem that the method is not sufficiently accurate for quantitative analysis.